Many modern wireless communication devices include multiple radios. These multiple radios may be used by the device to concurrently communicate via multiple wireless communication technologies. For example, many wireless communication devices include both a cellular radio for supporting communication over a cellular network and a wireless local area network (WLAN) radio, such as a Wi-Fi radio, for supporting communication over a WLAN. Such devices can accordingly communicate concurrently over both a cellular network and a WLAN. In many instances a device supporting concurrent connections to a cellular network and a WLAN can emit simultaneous transmissions via both the cellular radio and the WLAN radio.
Wireless communication devices are often subject to regulations limiting radio frequency (RF) emissions that are issued by government and other regulatory bodies, such as the Federal Communications Commission (FCC). For example, Specific Absorption Rate (SAR) restrictions, such as those issued by the FCC, place limits on the transmission power of wireless communication devices to limit the amount of RF energy radiated when the devices are in proximity to a human body (i.e., a device user). In this regard, SAR can be defined in terms of a measure of the rate at which energy is absorbed by the human body when exposed to an RF electromagnetic field. As such, SAR limits can be imposed that limit the total transmission power of a wireless communication device so as to limit RF absorption by a user of the device.
When multiple radios are transmitting concurrently in a multi-radio wireless communication device, the imposition of SAR restrictions and/or other regulations restricting total transmission power impose a requirement to jointly limit the transmission power of the concurrently transmitting radios. Present wireless communication devices generally apply a conservative approach that assumes a maximum transmission power for a higher transmission power radio, such as a cellular radio, and then decides a safe transmission power level for a lower transmission power radio, such as a WLAN radio (i.e., any remaining transmission power within the total transmission power limit after subtracting the maximum cellular transmission power from the total transmission power limit). As a cellular radio does not always transmit at its maximum possible transmission power, the WLAN radio is often penalized by transmitting at an overly conservative transmission power.